The present invention relates to an actuator with piezo-electric element and a method for producing the same, and more particularly to an actuator with piezo-electric element in various kinds of equipment, an ink-jet recording head using the actuator, and a method for producing the actuator.
Heretofore, actuators made of lead titanate zirconate (hereinafter called "PZT") have been used as ink-jet driving sources of ink-jet recording heads, that is, as actuators for converting electric energy into mechanical energy. Such an ink-jet recording head is equipped with desired elements including a head base where a number of separate ink passageways (e.g., ink cavities and ink reservoirs) are formed, a diaphragm mounted on the head base in such a way as to cover the whole ink passageway, lower electrodes attached to separate portions corresponding to the respective ink passageways of the diaphragm, electrode elements each having PZT films and upper electrodes, wiring formed:through an interlayer insulating film and so forth
The ink-jet recording head thus structured is so designed as to force out ink contained in the individual ink passageway from a nozzle plate provided for the individual ink-jet ink passageway by displacing the PZT film by applying an electric field to the PZT film.
The ink-jet recording head is usually manufactured through the following steps of: forming a thermal oxide film on a single crystal silicon substrate; then forming electrode elements including lower electrodes, PZT films and upper electrodes which are in desired shapes; further forming desired elements such as wiring connected to the electrode elements through an interlayer insulating film; forming a thermal oxide film on a side opposite to the side on which the electrode elements of the single crystal silicon substrate; selectively etching portions corresponding to the region where the electrode elements of the; single crystal silicon substrate are formed; and forming separate ink passageways (e.g., ink cavities and ink reservoirs). When the etching is conducted, a passivation film for protecting the elements is formed. Subsequently, the ink-jet, recording head is completed through the desired steps of, for example, installing a nozzle plate with ink discharge ports formed therein and so on.
In the conventional ink-jet recording heads, platinum or platinum alloy is normally used to form the upper and lower electrodes. However, platinum or platinum alloy is poor in reactivity and disadvantageous in that, for example, it has poor adhesion to the insulating and interlayer insulating films; therefore, these films tend to peel off the elements, thus developing problems of reducing the reliability of the actuator with the piezo-electric element and the like.
In the process of manufacturing the conventional ink-jet recording head, the passivation film is formed in order to protect the elements when the separate ink passageways are formed. Although a fluoroplastic film and a silicon oxide film, for example, are used as such a passivation film, the problem is that adhesion to the substrate where the elements are formed is insufficient. More specifically, the adhesive force between the platinum film and the fluoroplastic film and the adhesive force between the platinum film and the silicon oxide film, for example, are both fragile. Consequently, there develops a problem resulting in making insufficient the adhesion of the passivation film to the substrate when the contact area of the platinum film with the passivation film (the fluoroplastic film and the silicon oxide film). Incidentally, the passivation film is normally removed after the ink passageways are formed.
A high-concentration alkaline solution such as a potassium hydroxide aqueous solution ranging from 5 wt % to 40 wt % is used as an etching solution when etching is conducted to form the aforementioned ink passageways. When the etching solution is brought into contact with the elements at the time of etching, there is a problem arising from causing the elements to peel off the substrate or causing it to be damaged. More specifically, if the single crystal silicon substrate is etched so that the etching solution reaches the diaphragm (e.g., the silicon oxide film), the alkaline aqueous solution or an etching reaction product will transmit to the diaphragm, thus developing the problem of damaging the elements.